Quaternary ester ammonium compounds are rapidly biodegradable compounds which may therefore be used in various applications. However, they are also more subject to hydrolysis than are conventional quaternary ammonium compounds, e.g., ditallow dimethyl ammonium chloride. More particularly, during the preparation process of the quaternary ester ammonium compounds hydrolysis of the compounds may occur in the presence of water at high temperatures. These kind of side reactions have to be prevented, as they result in high amounts of impurities which reduce the hardness of the final composition.
Also, some of these quaternary ester ammonium compounds are hygroscopic, i.e., they have the ability to take up water. This results in caking of the compositions during storage and hydrolysis of the compounds. Although the storage temperature will be lower than the process preparation temperature, the period of time in storage is of course longer and, accordingly, hydrolysis cannot be prevented in the long term. A decrease in storage stability is the result.
With any solution to the above-mentioned problems, it has to be kept in mind that in all applications wherein quaternary ester ammonium compounds can be employed, it is preferred that the compound is added as pure as possible. Accordingly, if a second compound is necessary to prevent the above-mentioned disadvantages it should be present in the composition in an amount as low as possible. More particularly, the composition should comprise the quaternary ester ammonium compound in an amount as high as possible, i.e., the composition should have a high content of active matter.
In view of the above, it is one of the objects of the present invention to provide a process to prepare compositions comprising quaternary ester ammonium compounds with a very small amount of impurities. Also, it is an object to provide storage stable and non-caking compositions. Finally, it is an object to provide compositions comprising a high amount of quaternary ester ammonium compounds.
Various processes are known to prepare solid compositions comprising a quaternary ammonium compound and a fatty acid compound. WO 92/18593 discloses the preparation of a composition comprising a quaternary ester ammonium compound and a fatty acid compound in two ways. A first process comprises the steps of mixing the two compounds together by melting the fatty acid compound and subsequently mixing the quaternary ester ammonium compound in the molten fatty acid compound. A second process shows the quaternization of an ester amine compound in a molten fatty acid compound. Both processes have the disadvantage that the resulting compositions comprise a high amount of impurities which affect the properties of the compositions. Furthermore, the resulting solid compositions comprise the quaternary ester ammonium compound in an amount of 50 wt % or lower, preferably 5 to 30 wt %. Exemplified are compositions comprising at most 25 wt % of quaternary ester ammonium compound.
U.S. Pat. No. 4,840,738 discloses solid compositions comprising quaternary ester ammonium compounds and a second compound. This second compound is selected from potassium sulfate, micronized silica, and powdered urea. Fatty acid compounds are not mentioned. Furthermore, the quaternary ester ammonium compound is present in an amount up to 20 wt % in the composition. Finally, the disclosed preparation process comprises mixing the quaternary ester ammonium compound with the second compound. The latter is not added during the quaternization process.
JP-A-58011033 discloses agents to prevent solidification of inorganic salts. Among a list of agents quaternary ester ammonium compounds are mentioned, such as choline bitartrate, choline dihydrogen citrate, and choline gluconate. Optionally, the agents may be mixed with, among others, alkali salts of higher fatty acid compounds. However, mixtures of a quaternary ester ammonium compound and a fatty acid compound are not disclosed. Neither is mentioned in which quantities the compounds should be mixed. Finally, the object to achieve in the Japanese publication is to use the hygroscopic property of the agents to prevent solidification of the inorganic salts. This is the direct opposite from the object of the present invention to reduce the hygroscopic effect of the quaternary ester ammonium compound.
From EP-A-0445525 it is known to prepare a quaternary ether ammonium compound by carrying out the quaternization reaction in the presence of a relatively small amount of a water-alcohol solvent after which a fatty acid compound is added and the solvent is removed. Process temperatures range from 50-120.degree. C. Quaternary ester ammonium compounds are not disclosed.
Finally, EP-A-0704522 describes a dryer-activated fabric softening composition comprising quaternary ester ammonium compound and an unsaturated fatty acid having an iodine value (IV) of 3 to 60, preferably of 12 to 45. The unsaturated fatty acid is added to improve the processability of the composition, i.e., to reduce the viscosity and ease the handling, and improve the antistatic performance of the composition. Saturated fatty acids harm softening and/or antistatic performance. Examples are given of unsaturated fatty acids having iodine values of 40-50. This publication also relates to a process for preparing such compositions and to a process for preparing the quaternary ester ammonium compound. In this latter process, an unsaturated fatty acid having an IV of 3-60, preferably 8 to 50, is added during the quaternization in order to reduce and/or maintain the viscosity of the reaction mixture.
Furthermore, it has been established that the preparation of quaternary ester ammonium compounds cannot be carried out in the presence of water at these temperatures in view of the above-mentioned disadvantages.